Root-knot nematodes (Meloidogyne spp.) are plant pathogens that infect many hosts and cause extensive damage to crops throughout the world. In the southeastern United States, the Southern Root Knot Nematode (Meloidogyne incognita), herein referred to as SRKN, is a major pest of soybean (Glycine max (L)). Restrictions on the use of nematicides including cancellation of DBCP (1,2-dibromo3-chloropropane) and EDB (ethylene dibromine) have encouraged development of alternative methods of SRKN control (Harris et al. Crop Sci. 43:1848-1851 (2003)). Growing SRKN-resistant soybean cultivars is the most effective means of reducing losses in yield and growers' profits due to the parasite (Li et al., Theor Appl Genet 103:1167-1173 (2001)). Therefore, a number of SRKN-resistant cultivars have been developed (Ha et al., Crop Science 44:758-763 (2004)).
Both elite soybean varieties and accession germplasm have been examined for SRKN resistance. Two sources of SRKN resistance are PI 96354 and Palmetto. Phenotypic screening of 2,370 soybean accessions from the USDA Soybean Germplasm Collection (Urbana, Ill.) identified PI 96354 as the most highly resistant source in the collection (Luzzi, et al. Crop Sci. 27:258-262 (1987)). Crossing the highly SRKN resistant variety PI 96354 with the SRKN susceptible Bossier allowed for mapping a major quantitative trait loci (QTL) for SRKN resistance to linkage group (LG) O and a minor QTL to LG-G of the publicly available soybean genetic linkage map (Tamulonis et al., Crop Sci. 37: 1903-1909 (1997)). Forrest is another soybean variety which exhibits resistance to SRKN and has been used as a parental source of SRKN resistance in the development of soybean varieties. The ancestral source of SRKN resistance in Forrest and many other elite varieties is considered to be Palmetto (Ha et al. Crop Sci. 44:758-763 (2004)). A major SRKN resistance QTL Rmi was identified in studies with a cross of Forrest with the susceptible Bossier (Luzzi et al., J Heredity 85:484-486 (1994)). Pedigree analysis of forty-eight soybean varieties and genotyping using simple sequence repeats (SSRs) markers provided evidence that SRKN resistant varieties inherited a major SRKN resistant QTL (Rmi) on Linkage Group O from ancestral resistant sources (Ha et al. Crop Sci. 44:758-763 (2004)).
Breeding for SRKN resistant soybeans can be greatly facilitated by the use of marker-assisted selection for SRKN resistance QTL. Single nucleotide polymorphisms (SNPs) and (SSRs) can be used as genetic markers to locate QTL associated with SRKN resistance. SNPs are preferred a because technologies are available for automated, high-throughput screening with SNP marker platforms, which can decrease the time to select for and introgress SRKN resistance in soybean plants. Further, SNP markers are ideal because the likelihood that a particular SNP allele is derived from independent origins in the extant populations of a particular species is very low. As such, SNP markers are useful for tracking and assisting introgression of SRKN resistance alleles, particularly in the case of SRKN resistance haplotypes. SNP markers can be used to screen for SRKN resistance QTL on LG-O and LG-G of the soybean genetic linkage map (Ha et al., Crop Sci. 47(2) S73-S82 (2007)).
The present invention provides and includes methods and compositions for screening and selecting a soybean plant comprising the SRKN resistance QTL.